The present invention relates generally to a method and an apparatus for filtering impurities out of a fluid, and more particularly to a method and an apparatus for filtering impurities out of lubrication oil for use in an internal combustion engine.
In various kinds of apparatuses utilizing an oil pressure and lubrication oil, various kinds of fine particulate impurities such as metal powders and carbon particles are inherently mixed in the oil. If such impurities are not removed, there might occur various drawbacks such as defect of apparatuses, leakage of oil and increase in temperature. Therefore, the duration of the oil is shortened and the oil has to be exchanged by new one frequently. In order to avoid such drawbacks, there have been proposed various kinds of filtering systems.
In the most usual filtering systems, there is provided a filtering circulation system separately from a main circulation system and a filter having a filtering element of relatively high density is arranged in the filtering circulation system. Then, the oil is forcedly flowed by a pump through the filter to remove impurities contained in the oil. This known oil cleaning system requires the pump and thus there might occur another problem that the energy loss is large.
It is also known that a part of the pressed oil is by-passed from the main circulation system through a valve for regulating the oil flow rate and is forced to pass through the filter of high density, and then the filtered oil is returned into an oil tank. In such an oil cleaning system, since a part of the oil has to be by-passed from the main circulation system, an amount of the oil must be increased than necessity. Therefore, this known oil cleaning system is not economical.
It has been generally known to insert the filter in the main circulation system. In such a system, since the filter provides a very high resistance against the flow of the oil, a very high pressure is generated in the system and thus a pipe line and filter must have a high mechanical strength. Therefore, in usual systems the filters of low density have to be used. Then, it is impossible to remove fine impurities effectively. In generaly, such fine particles affect the system to the greatest extent.
In order to avoid the above mentioned drawbacks, it has been further known to provide a filter having a large area so as to decrease an apparent resistance of the filter or to provide a fine filter in a by-path circuit. However, it is necessary to flow the oil forcedly through the by-path circuit, because the by-path circuit has a great resistance. Therefore, also in this known system, a pump has to be arranged to flow the oil through the by-path circuit and thus the energy loss occurs.
In general, in an internal combustion engine there has been widely used a lubricating system shown in FIG. 1. A lubrication oil contained in an oil tank 2 is flowed by a pump 1 into an engine 3 to be lubricated and then is returned into the oil tank 2. In an oil circulating path is arranged a filtering system. Usually, the filtering system comprises a sub-filter 4 called a strainer and a main filter 5 provided on sucking and discharging sides of the pump 1, respectively. In an automobile, the main filter 5 is formed as a cartridge and is detachably secured to an engine block 11 as illustrated in FIG. 2. These filters 4 and 5 are provided in a path through which the lubricating oil is supplied to the engine 3. In order to protect the lubricating system from the blockage and abnormal pressure increase due to increase in viscosity of the oil at a low temperature, the main filter 5 comprises a low density filtering material 12 such as a porous filtering paper. This is to say, the main filter 5 is a coarse filter which could not remove fine particles effectively.
In the known system shown in FIG. 1, there is further provided a relief valve 6 in parallel with the main filter 5. When the main filter 5 is blocked, the oil is automatically flowed through the valve 6 into the engine 3. Then the oil containing fine impurities which could not be removed by the strainer 4 is introduced into the engine 3. Therefore, it is recommended that the lubrication oil used in the automobile engine should be exchanged by a new oil every 5,000 km running. If the contaminated oil is further used, there might occur serious problems that the impurities might be introduced into slidable portions and bearings to cause the friction, and the fine particles might be deposited inside fine conduits of the oil circulation system to prevent the smooth flow of the oil and to cause the lack of lubrication. In FIGS. 1 and 2, reference numerals 9 and 10 denote a pressure adjusting valve and a pressure gauge or a pressure alarm, and reference numerals 8a and 8b are inlet and outlet conduits of the main filter 5.
In the internal combustion engine installed in automobile there is sometimes provided a turbo charger driven by an exhausted gas turbine in view of saving the resources and energy. Further, diesel engines using a light oil as a fuel are also used in some automobiles. In the turbo charger, the turbine is rotated at a high speed such as 10,000 rpm by means of exhausted gas of high temperature, and thus it is required to supply into bearings of the turbine the lubricating oil as clean as possible. In the diesel engine, the light oil generates a log of carbon particles which are liable to be mixed in the lubrication oil. Further, when sulphurous components in the light oil are burnt, sulphurous acid gas is produced. When the sulphurous acid gas is combined with a water contained in the exhausted gas, there is produced sulfuric anhydride having a strong etching action. When the sulfuric anhydride is mixed with the lubrication oil, metal portions, particularly bearing alloy portions are seriously attacked.
As illustrated in FIG. 1, in order to remove various kinds of inpurities out of the lubrication oil, it is also known to provide an auxiliary path including a high density filter 7 from the downstream of the pump 1 to the oil tank 2. By providing such an auxiliary filtering path, the lubrication oil can be cleaned effectively and can be used for a much longer time. However, such a system could be applied only to large internal combustion engines, That is to say, when the system including the axuiliary filter 7 is applied to the existent small engines, one encounters the following difficulties.
(1) Machinery work for dividing a part of the lubrication oil from the inlet conduit 8a of the main filter 5 to the auxiliary filter 7 is difficult.
(2) Machinery work for returning the oil cleaned by the auxiliary filter 7 is additionally required.
(3) Since the auxiliary filtering path including the auxiliary filter 7 undertakes a part of the oil, when the resistance of the main filter 5 is increased, an amount of the oil supplied to the engine 3 becomes small and thus there occurs a danger of lack of lubrication.
Owing to the above difficulties, the auxiliary filter 7 has not been widely adopted in the small internal combustion engines for automobiles.
The inventor has found that even if the lubrication oil has been contaminated with the fine particles, the lubrication property of the oil has not been lost. Therefore, if it is possible to remove the fine particles, the oil could still be used. Nowadays, due to the improvement of the refining technique and the development of high molecular additives and synthetic lubrication oil, the oil is scarcely degraded due to the high temperature and the usable life time of the oil has been prolonged. Under the above circumstance, it is quite advantageous to remove the fine impurities from the oil effectively.